Electrostatic actuator and method of driving the same

ABSTRACT

A first stator is provided with stator electrodes sequentially arranged in a predetermined direction. An extended electrode is mounted on a second stator arranged to face the first stator. A slider is movably arranged between the first and second stators. The slider is provided with a large number of slider electrodes arranged to face the stator electrodes and a second slider electrode facing the extended electrode. The slider electrodes are maintained at the ground potential. A first and second driving voltage are periodically applied to the stator electrodes and to the extended electrode, respectively, which are opposite to each other in phase and are periodically switched between the ground potential and the positive driving voltage. Thus, the slider is moved in a direction while being vibrated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 09/818,840filed Mar. 28, 2001 now U.S. Pat. No. 6,670,738, which is now allowed,and claims priority to the Japanese Application no. 2000-094569, filedMar. 30, 2000, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to an electrostatic actuator for driving aslider or a movable section with an electrostatic force and a method ofdriving the same, particularly, to an electrostatic actuator having animproved simple structure and capable of driving the slider or themovable section with a high accuracy and a method of driving the same.

The electrostatic actuator for driving a slider or a movable section hasalready been disclosed in some publications, e.g., Japanese PatentDisclosure (Kokai) No. 8-140367, and “Electrostatic Linear MicroactuatorMechanism, JOURNAL OF LIGHTWAVE TECHNOLOGY, Vol. 17, No. 1, January1999, IEEE”. The actuator disclosed in these publications comprises anarray of electrodes as shown in FIG. 1. In this electrostatic actuator,a slider or a movable section 102 is arranged slidable forward asdenoted by an arrow 101 or backward between two stators 103A and 103Barranged to face each other. An electrode section 104 is provided on theslider 102. Two systems of stator electrodes 106A and 106C to whichvoltage is applied at different timings are alternately arranged on thestator 103A. Likewise, two systems of electrodes 106B and 106D to whichvoltage is applied at different timings are arranged on the other stator103B. The electrodes 106A to 106D provided on the stators 103A, 103B andthe electrode section 104 of the slider 102 are substantially equal toeach other in the pitch and the electrode width. Also, the electrodes106A, 106C of the stator 103A and the electrodes 106B, 106D of thestator 103B are arranged such that the phase of the arrangement isshifted by ½.

If a voltage is applied from a voltage source (not shown) to theelectrode 106A in the electrostatic actuator of the particularconstruction, an electrostatic force, i.e., Coulomb force, is generatedbetween the electrode 106A and the electrode section 104, with theresult that the slider 102 is attracted toward the stator 103A such thatthe electrode 106A and the electrode section 104 are allowed to faced toeach other. Then, when the switching circuit (not shown) for supplying avoltage is switched to change the electrode to which a voltage issupplied from the electrode 106A to the electrode 106B so as to supply avoltage to the electrode 106B, the slider 102 is attracted toward theother stator 103B such that the electrodes 106B and the electrodesection 104 are allowed to faced to each other. Also, when the switchingcircuit is switched to change the electrode to which a voltage issupplied from the electrode 106B to the electrode 106C so as to supply avoltage to the electrode 106C, the slider 102 is attracted toward thestator 103A again such that the electrodes 106C and the electrodesection 104 are allowed to faced to each other. Further, when theswitching circuit is switched to change the electrode to which a voltageis supplied from the electrode 106C to the electrode 106D so as tosupply a voltage to the electrode 106D, the slider 102 is attractedtoward the stator 103B again such that the electrodes 106D and theelectrode section 104 are allowed to faced to each other. As describedabove, if a voltage is applied successively to the electrodes 106A,106B, 106C and 106D, the slider 102 is vibrated microscopically betweenthe stators 103A and 103B and is macroscopically driven in the forwarddirection as denoted by the arrow 101 in FIG. 1. If the order ofapplying a voltage to the electrodes is reversed such that the voltageis applied to the electrodes 106D, 106C, 106B and 106A in the ordermentioned, the slider 102 is driven in the backward direction oppositeto the forward direction denoted by the arrow 101 in FIG. 1.

In the electrostatic actuator described above, it is necessary for thepair of stators 103A and 103B to be aligned with a high accuracy. It isalso necessary for the electrodes of the same width to be formedequidistantly with a high accuracy in the stators 103A, 103B. Naturally,a sufficient time and labor are required for manufacturing the parts ofthe electrostatic actuator and for assembling these parts with a highaccuracy, leading to a high manufacturing cost of the actuator. Thisproblem of the high manufacturing cost must be overcome for realizing amass production of the actuator.

A method of applying voltage and the operating principle of theconventional electrostatic actuator will now be described with referenceto FIG. 1. Incidentally, those members of the actuator, which aresubstantially same as those shown in FIG. 1 are denoted by the samereference numerals in FIG. 2 for avoiding the overlapping description.

As described above with reference to FIG. 1, if a voltage is appliedsuccessively to the electrodes 106A to 106D provided on the stators 103Aand 103B, the slider 102 is driven so as realize a linear movement on amacroscopic level. In the electrostatic actuator shown in FIG. 2, theelectrodes 106A and 106B are covered with a dielectric film 105 so as toprevent these electrodes 106A, 106B from the insulation breakdown, asdisclosed in Japanese Patent Disclosure No. 8-140367 referred topreviously.

If a voltage is applied first to the electrode 106A as shown in FIG. 2,dielectric polarization 107 is generated in a dielectric film 105covering the electrode 106A. Then, if a voltage is applied to theelectrode 106B, the slider 102 is attracted toward the other stator 103Bso as to be driven such that the electrode section 104 is allowed toface the electrode 106B. It should be noted, however, that the componentof the dielectric polarization generated in the dielectric film 105mounted on the electrode 106A produces the function of keeping theslider 102 attracted toward the stator 103A. The component of the forceproduced by the dielectric polarization 107 is very small in terms ofthe potential level. However, since the distance between the stator 103Aand the electrode section 104 of the slider 102 is short, it is possiblefor the force generated by the dielectric polarization 107 not to benegligible as a force for inhibiting the movement of the slider 102.This is based on the fact that the electrostatic force is inverselyproportional to the square of the distance between the electrodes. Underthe circumstances, the driving of the slider 102 tends to be unstable inthe conventional electrostatic actuator. It should also be noted thatthe degree of the charge leakage in the dielectric film 105, i.e., thetime for the dielectric polarization to disappear, is not constant,which also provides a cause of the failure for the movement of theslider 102 to be made constant.

As described above, in the conventional electrostatic actuator, it isnecessary to align accurately the two stators 103A and 103B so as toprovide accurately a desired phase of arrangement of these two stators.It is also necessary to form accurately the electrodes facing the twosurfaces of the slider or movable element 102. It follows that a longtime and much labor are required for assembling the actuator, leading toa high manufacturing cost. In other words, serious problems must besolved before the mass production of the actuator is realized.

It should also be noted that, in the conventional electrostaticactuator, the driving operation of the slider 102 tends to becomeunstable because of the influence produced by the dielectricpolarization taking place in the dielectric film covering the electrode.

What should also be noted is that the degree of the charge leakage inthe dielectric film 105, i.e., the time for the dielectric polarizationto disappear, is not constant, which also provides a cause of thefailure for the movement of the slider 102 to be made constant.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide an electrostaticactuator, which permits improving the assembling efficiency and the massproduction capability and also permits the slider to make a stablemicroscopic movement with a relatively high accuracy.

According to a first aspect of the present invention, there is providedan electrostatic actuator mechanism, comprising:

a first stator provided with an electrode group including at least threeelectrodes successively arranged in a predetermined direction, voltagebeing applied to the electrodes in different order;

a second stator arranged to face the first stator and provided with aplanar electrode extending in the predetermined direction;

a movable member arranged between the first stator and the secondstator, and provided with a first electrode section facing the electrodegroup and a second electrode section facing the planar electrode; and

a switching circuit configured to apply voltage alternately to theelectrode group and the planar electrode, the potential of any of theelectrodes forming the electrode group being rendered higher than thepotential of the first electrode section, or the potential of the planarelectrode being rendered higher than the potential of the secondelectrode section, and to switch the order of applying voltagesuccessively to the first electrode group.

It is possible for the electrostatic actuator of the present inventionto further comprise a dielectric film formed to cover the electrodegroup.

It is also possible for the electrostatic actuator of the presentinvention to further a dielectric film formed to cover the firstelectrode section.

Further, where the dielectric film is formed, it is possible for theelectrostatic actuator of the present invention to further comprise acircuit configured to impair a potential difference such that thepotential of the electrode group is rendered lower than the potential ofthe first electrode section, when voltage is applied to the planarelectrode.

It is possible for that the slider having a surface which isperpendicular to the predetermined direction to form an optical elementsurface.

It is possible for the first and second stators to have stoppersprojecting from the upper surfaces of the electrode group and the planarelectrode, and for the movable member to be provided with regions inwhich the stoppers are slid, the region being formed on the surfaces onwhich the first and second electrode sections are formed.

Also, it is possible for the movable member to have stoppers projectingfrom the surfaces of the first and second electrode sections, and forthe first and second stators to be provided with regions in which thestoppers are slid, the regions being formed on the surfaces on which theelectrode group and the planar electrode are formed.

Further, it is possible for the first stator to include a first part andfor the second stator to include a second part, the first and secondparts being connected to each other to form a stator.

According to a second aspect of the present invention, there is provideda method of driving an electrostatic actuator mechanism including afirst stator having an electrode group including at least threeelectrodes successively arranged in a predetermined direction, voltagebeing applied to the electrodes in different order, a second statorarranged to face the first stator and having a planar electrodeextending in the predetermined direction, and a movable member arrangedbetween the first stator and the second stator and having a firstelectrode section facing the electrode group and a second electrodesection facing the planar electrode, the method comprising:

applying voltage to the electrode group, the potential of any of theelectrodes forming the electrode group being rendered higher than thepotential of the first electrode section;

applying voltage to the planar electrode, the potential of the planarelectrode being rendered higher than that of the second electrodesection;

applying voltage by switching the electrode of the first electrode groupsuch that the potential of the switched electrode is rendered higherthan the potential of first electrode section;

applying voltage such that the potential of the planar electrode isrendered higher than the potential of the second electrode section; and

repeating the voltage application defined above.

Further, according to a third embodiment of the present invention, thereis provided a camera module, comprising:

a image pick-up element; and

an electrostatic actuator mechanism mounted to the image pick-upelement, the electrostatic actuator mechanism including;

a first stator provided with an electrode group including at least threeelectrodes successively arranged in a predetermined direction, voltagebeing applied to the electrodes in different order,

a second stator arranged to face the first stator and provided with aplanar second electrode extending in the predetermined direction,

a movable member arranged between the first stator and the secondstator, and provided with a first electrode section facing the electrodegroup, a second electrode section facing the planar electrode, and anoptical element configured to form an optical image on the image pick-upelement, and

a switching circuit configured to apply voltage alternately to theelectrode group and the planar electrode, the potential of any of theelectrodes forming the electrode group being rendered higher than thepotential of the first electrode section, or the potential of the planarelectrode being rendered higher than the potential of the secondelectrode section, and to switch the order of applying voltagesuccessively to the electrode group.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 a cross sectional view schematically showing the construction ofa conventional electrostatic actuator;

FIG. 2 is a cross sectional view schematically showing the constructionof a conventional electrostatic actuator provided with a dielectricfilm;

FIG. 3 is a block diagram schematically showing the construction of anelectrostatic actuator according to one embodiment of the presentinvention;

FIGS. 4A to 4E are timing charts each showing a voltage signal appliedto the electrodes of the electrostatic actuator shown in FIG. 3;

FIGS. 5A to 5E are cross sectional views collectively showing how todrive the electrostatic actuator according to a modification of theembodiment shown in FIG. 3;

FIGS. 6A to 6E are timing charts each showing a voltage signal appliedto the electrodes of the electrostatic actuator in relation to thedriving method shown in FIGS. 5A to 5E;

FIG. 7 is a cross sectional view schematically showing the constructionof an electrostatic actuator according to another modified embodiment ofthe present invention;

FIG. 8 is a cross sectional view for schematically explaining theoperating principle of the electrostatic actuator shown in FIG. 7;

FIGS. 9A to 9F are timing charts each showing a voltage signal appliedto the electrodes of the electrostatic actuator shown in FIGS. 7 to 8;

FIG. 10 is a graph showing the relationship between the displacement,with a gap in the electrostatic actuator shown in FIGS. 7 and 8 used asa parameter, and the driving force imparted to the slider;

FIG. 11 is a cross sectional view schematically showing the constructionof an electrostatic actuator according to another modified embodiment ofthe present invention;

FIGS. 12A and 12B are views relating to the electrode width of theslider of the electrostatic actuator shown in FIG. 11 and also relatingto the operation of the slider;

FIGS. 13A and 13B are cross sectional views schematically showinganother modified embodiment of the electrostatic actuator shown in FIG.3;

FIGS 14A to 14E are timing charts each showing a voltage signal appliedto the electrodes of the electronic actuator shown in FIGS. 13A and 13B;

FIGS. 15A and 15B are cross sectional views schematically showinganother modified embodiment of the electrostatic actuator shown in FIG.3;

FIG. 16 is a perspective view schematically showing another modifiedembodiment of the electrostatic actuator shown in FIG. 3;

FIGS. 17A to 17C are perspective views schematically showingcollectively the manufacturing process of a slider according to anothermodified embodiment of the electrostatic actuator shown in FIG. 3;

FIGS. 18A and 18B are a cross sectional view and a broken view,respectively, schematically showing collectively the construction of anelectrostatic actuator provide with a stopper according to anotherembodiment of the present invention;

FIGS. 19A and 19B are a cross sectional view and a broken view,respectively, schematically showing collectively the construction of anelectrostatic actuator provide with a stopper according to anotherembodiment of the present invention;

FIG. 20 is a perspective view schematically showing in a dismantledfashion the construction of an electrostatic actuator provided with astopper according to another modified embodiment of the presentinvention;

FIGS. 21A to 21C are a plan view and cross sectional views collectivelyshowing schematically the construction of the stator of an electrostaticactuator according to another embodiment of the present invention;

FIGS. 22A to 22D are cross sectional views collectively showingschematically the manufacturing process of the stator of anelectrostatic actuator according to another embodiment of the presentinvention;

FIGS. 23A to 23C are a plan view and two cross sectional viewscollectively showing schematically the construction of the stator of anelectrostatic actuator according to another embodiment of the presentinvention;

FIGS. 24A to 24C are a plan view and two cross sectional viewscollectively showing schematically the construction of the stator of anelectrostatic actuator according to another embodiment of the presentinvention;

FIGS. 25A to 25D are a plan view, two cross sectional views, and a backview collectively showing schematically the construction of the statorof an electrostatic actuator according to another embodiment of thepresent invention;

FIGS. 26A to 26D are a plan view, two cross sectional views, and a backview collectively showing schematically the construction of the statorof an electrostatic actuator according to another embodiment of thepresent invention;

FIGS. 27A to 27D are a plan view, two cross sectional views, and a backview collectively showing schematically the construction of the statorof an electrostatic actuator according to another embodiment of thepresent invention;

FIGS. 28A to 28C are a plan view and two cross sectional viewscollectively showing schematically the construction of the stator of anelectrostatic actuator according to another embodiment of the presentinvention;

FIGS. 29A to 29D are a plan view, two cross sectional views, and a backview collectively showing schematically the construction of the statorof an electrostatic actuator according to another embodiment of thepresent invention; and

FIG. 30 is a perspective view schematically showing a focus controlmechanism as an application of an electrostatic actuator of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of an electrostatic actuator of the presentinvention will now be described in detail with reference to theaccompanying drawings.

Specifically, FIGS. 3 to 6 show an electrostatic actuator according toone embodiment of the present invention. In the electrostatic actuatorshown in FIG. 3, a first stator 2A and a second stator 2B are arrangedto face each other, and a slider or movable section 3 is slidablyarranged between the first and second stators 2A and 2B. It is possiblefor the first and second stators 2A and 2B to be shaped like a flatplate or like a semicircular cylindrical plate. Where the first andsecond stators 2A and 2B are shaped like a flat plate, the slider 3 isin the form of a block or a hollow block having flat surfaces facing thefirst and second stators 2A and 2B. Where the first and second stators2A and 2B are shaped like a semicircular cylindrical plate, the slider 3is in the form of a column or a hollow cylinder conforming with theshapes of the first and second stators 2A and 2B.

The electrostatic actuator shown in FIG. 3 comprises a first stator 2Ahaving a three line type construction in which a driving signal issupplied at a different timing to the three stator electrodes 22A, 22B,22C through three electrical signal lines. Specifically, each of thefirst, second and third striped stator electrodes 22A, 22B, 22C has acomb like shape and the first, second and third striped statorelectrodes 22A, 22B, 22C are alternately arranged on the surface of thefirst stator 2A in the sliding direction of the slider 3, i.e., in aforward direction 24 and a backward direction opposite to the forwarddirection 24. In addition, these first, second and third statorelectrodes 22A, 22B, 22C are arranged at the same pitch Ph. These first,second and third stator electrodes 22A, 22B, 22C are arranged over arange within which at least the slider 3 is slid. On the other hand, anextended surface electrode 26D that extends flat is formed on thesurface of the second stator 2B in a manner to extend flat.

The slider 3 has a surface facing the first stator 2A, and first sliderelectrodes 30A are arranged on the surface of the slider 3 in a mannerto face the first stator 2A at a pitch Ph equal to the pitch Ph at whichthe first, second and third stator electrodes 22A, 22B, 22C arearranged. The slider 3 also has a surface facing the second stator 2B,and the second slider electrode 30D that extends flat is formed on theparticular surface of the slider 3.

The first, second and third stator electrodes 22A, 22B, 22C arealternatively arranged in this order, with the phase of the arrangement(phase of the arrangement in which the arranging pitch corresponds to 3Ph) of the electrodes deviated by ⅓ (=Ph). Also, the first sliderelectrodes 30A of the slider 3 may be formed by forming projections andrecesses on the surface of a conductor, as shown in FIG. 3.Alternatively, it is possible to form the first slider electrodes 30A byuniformly forming a conductive material layer on a flat surface,followed by patterning the conductive material layer in a desired pitch.

As shown in FIG. 3, the first, second, third stator electrodes 22A, 22B,22C, the extended surface electrode 26D, and the second slider electrode30D are connected to a voltage source 42 generating a voltage via aswitching circuit 40 serving to determine the timing at which a voltageis applied to these stator electrodes 22A, 22B, 22C, and the extendedelectrode 26D. Also, the first slider electrode 30A and the secondslider electrode 30D are connected to the ground via the switchingcircuit 40 or are connected to a negative potential point. The switchingcircuit 40 is substantially equal in the circuit construction to thecircuit shown in FIG. 8, which is to be referred to herein later.Specifically, the switching circuit 40 comprises a stationary contact ora grounded contact connected to the stator electrodes 22A, 22B, 22C andthe extended electrode 26D, a first movable contact connected to avoltage source 42, which is connected to these stationary contacts, anda second movable contact that is grounded to connected to a negativepotential point. When one of these stationary contacts is connected tothe voltage source 42 via the first movable contact in the switchingcircuit 40 of the particular construction, the other stationary contactsare connected to the ground via the second movable contact or connectedto a negative potential point.

In the electrostatic actuator shown in FIG. 3, the slider 3 is moved inthe forward direction 24 or a backward direction opposite to the forwarddirection 24 by the driving principle described below.

In the first step, a voltage, i.e., a high level voltage or potential,is applied to the first stator electrode 22A mounted to the stator 2A asshown in FIG. 4A, and the first slider electrode 30A and the secondslider electrode 30B mounted to the slider 3 are connected to the groundor maintained at a potential lower than a potential on the statorelectrode 22A, i.e., a low level voltage or potential as shown in FIG.4E. If the potential of the first stator electrode 22A is set higherthan the potential of the first slider electrode 30A mounted to theslider 3, and if the other stator electrodes 22B, 22C, and the secondslider electrode 30D are connected to the ground or to a low levelvoltage or potential point, an electrostatic force, i.e., Coulomb force,is generated between the first stator electrode 22A and the first sliderelectrode 30A, with the result that the slider 3 is attracted toward thefirst stator 22A such that the first slider electrode 30A is attractedtoward the stator electrode 22A. To be more specific, since the statethat the first stator electrode 22A and the first slider electrode 30Aare allowed to exactly overlap each other is most stable, the slider 3receives force from the first stator electrode 22A such that the firststator electrode 22A and the first slider electrode 30A are allowed toface each other as denoted by an arrow 44. Then, if the voltage-applyingelectrode is switched from the first stator electrode 22A to theextended electrode 26D, which extends flat, by the operation of theswitching circuit 40, a high level voltage is applied to the extendedelectrode 26D and the other electrodes are maintained at a low levelvoltage, as shown in FIG. 4D. As a result, the slider 3 is moved awayfrom the first stator electrode 22A so as to be attracted toward thesecond stator 2B.

Also, if the voltage-applying electrode is switched from the extendedelectrode 26D to the stator electrode 22B mounted to the stator 2 by theoperation of the switching circuit 40, a voltage is applied to thesecond stator electrode 22B, as shown in FIG. 4B. As a result, anelectrostatic force, i.e., Coulomb force, is generated between thesecond stator electrode 22B and the first slider electrode 30A asdenoted by an arrow 46, as in the case where a voltage is applied to thefirst stator electrode 22A, thereby attracting the slider 3 toward thefirst stator 2A such that the first slider electrode 30A is allowed tooverlap with the stator electrode 22B. If the voltage-applying electrodeis switched in the next step from the second stator electrode 22B to theextended electrode 26D by the operation of the switching circuit 40, asshown in FIG. 4D, the slider 3 is moved away from the second statorelectrode 22B so as to be attracted toward the second stator 2B.

Further, if the voltage-applying electrode is switched from the extendedelectrode 26D to the third stator electrode 22C by the operation of theswitching circuit 40, a voltage is applied to the third stator electrode22C, as shown in FIG. 4C. As a result, an electrostatic force, i.e.,Coulomb force, is generated between the third stator electrode 22C andthe electrode 30A as in the case of applying a voltage to each of thefirst and second stator electrodes 22A and 22B, with the result that theslider 3 is attracted toward the first stator electrode 22A such thatthe electrode 30A is allowed to overlap with the electrode 22C. Then, ifthe voltage-applying electrode is switched from the third statorelectrode 22C to the extended electrode 26D by the operation of theswitching circuit 40, a voltage is applied to the extended electrode26D, with the result that the slider 3 is moved away from the thirdstator electrode 22C so as to be attracted toward the second stator 2B.

If the sequence of the voltage application, in which the voltage isapplied to the first stator electrode 22A, the extended electrode 26D,the second stator electrode 22B, the extended electrode 226D, the thirdstator electrode 22C and the extended electrode 26D in the ordermentioned and, then, to the first stator electrode 22B, again, asdescribed above, is repeated as shown in FIGS. 4A to 4D, the slider 3 ismoved in the forward direction 24, i.e., in the direction of arrangementof the electrodes mounted to the first stator 2A on a macroscopic level,while the slider 3 is vibrated in a direction crossing the forwarddirection 24 on a microscopic level.

In the sequence described above, the slider 3 is moved in the forwarddirection 24. Where the slider 3 is moved in a backward directionopposite to the forward direction 24, a voltage is applied to theelectrodes in the order opposite to that described above. Specifically,a voltage is applied first to the third stator electrode 22C as shown inFIG. 4C, with the first slider electrode 30A and the second sliderelectrode 30D maintained at a low level potential as shown in FIG. 4E.It follows that the slider 3 is attracted toward the first stator 2A bythe electrostatic force, i.e., Coulomb force, generated between thethird stator electrode 22C and the electrode 30A such that the electrode30A is attracted toward the electrode 22C. Then, the voltage-applyingelectrode is switched from the third stator electrode 22C to theextended electrode 26C by the operation of the switching circuit 40 soas to apply a voltage to the extended electrode 26D as shown in FIG. 4D,with the result that the slider 3 is moved away from the third statorelectrode 22C so as to be attracted toward the second stator 2B.

Then, the voltage-applying electrode is switched from the extendedelectrode 26D to the second stator electrode 22B by the operation of theswitching circuit 40 so as to apply a voltage to the second statorelectrode 22B as shown in FIG. 4B, with the result that the slider 3 isattracted toward the first stator 2A by the electrostatic forcegenerated between the second stator electrode 22B and the first sliderelectrode 30A. Further, the voltage-applying electrode is switched fromthe second stator electrode 22B to the extended electrode 26D by theoperation of the switching circuit 40 so as to apply a voltage to theextended electrode 26D as shown in FIG. 4D, with the result that theslider 3 is moved away from the second stator electrode 22B so as to beattracted toward the second stator 2B.

In the next step, the voltage-applying electrode is switched from theextended electrode 26D to the first stator electrode 22A by theoperation of the switching circuit 40 so as to apply a voltage to thefirst stator electrode 22A as shown in FIG. 4A, with the result that theslider 3 is attracted toward the first stator 2A by the electrostaticforce generated between the first stator 22A and the electrode 30A.Then, the voltage-applying electrode is switched from the first statorelectrode 22A to the extended electrode 26D by the operation of theswitching circuit 40 so as to apply a voltage to the extended electrode26D as shown in FIG. 4D, with the result that the slider 3 is moved awayfrom the third stator electrode 22C so as to be attracted toward thesecond stator 2B.

In the sequence of the movement of the slider 3 in the backwarddirection described above, a voltage is applied to the third statorelectrode 22C, the extended electrode 26D, the second stator electrode22B, the extended electrode 26D, the first stator electrode 22A and theextended electrode 26D in the order mentioned and, then, the voltage isapplied again to the third stator electrode 22C. If the sequencedescribed above is repeated, the slider 3 is moved in a directionopposite to the forward direction 24, i.e., in the direction of thearrangement of the electrodes mounted to the first stator 2A, while theslider 3 is vibrated in a direction crossing the forward direction 24.

In the electrostatic actuator described above, the extended electrode26D mounted to the second stator 2B is a single electrode of a simplestructure, which simply extends flat. Therefore, the alignment betweenthe extended electrode 26D and the first to third stator electrodes 22A,22B, 22C is not required. Also, the electrostatic actuator is simple inconstruction, leading to improvements in the assembling operation and inthe mass production capability.

A method of driving an electrostatic actuator according to amodification of the embodiment described above will now be describedwith reference to FIGS. 5A to 5E and 6A to 6E.

Specifically, FIGS. 5A to 5E are directed to a method of driving theelectrostatic actuator shown in FIG. 3, which is directed to a modifiedembodiment of the present invention, and show the relationship betweenthe timing of the voltage application to the electrodes and the movementof the slider 3.

In the first step, a voltage is applied to the first stator electrode22A, as shown in FIG. 6A, with the first slider electrode 30A and thesecond slider electrode 30D maintained at a low level, as shown in FIG.6E. As a result, the slider 3 is attracted toward the first stator 2Asuch that the first slider electrode 30A is pulled by the first statorelectrode 22A by the electrostatic force generated between the firststator electrode 22A and the electrode 30A, as shown in FIG. 5A. Then,the voltage-applying electrode is switched from the first statorelectrode 22A to the extended electrode 26D by the operation of theswitching circuit 40 so as to apply a voltage to the extended electrode26D as shown in FIG. 6D, with the result that the slider 3 is moved awayfrom the third stator electrode 22C so as to be attracted toward thesecond stator 2B, as shown in FIG. 5B.

In the next step, the voltage-applying electrode is switched from theextended electrode 26D to the first and second stator electrodes 22A,22B by the operation of the switching circuit 40 so as to apply avoltage to the first and second stator electrodes 22A, 22B as shown inFIGS. 6A and 6B, with the result that the slider 3 is attracted towardthe first stator 2A by the electrostatic force generated between thefirst and second stator electrodes 22A, 22B and the first sliderelectrode 30A, as shown in FIG. 5C. It should be noted that, since avoltage is applied to both the first and second stator electrodes 22Aand 22B as shown in FIGS. 6A and 6B, the slider 3 is attracted towardthe first stator 2A such that the first slider electrode 30A ispositioned to face the first and second stator electrodes 22A, 22B, asshown in FIG. 5C. Then, the voltage-applying electrode is switched fromthe first and second stator electrodes 22A, 22B to the extendedelectrode 26D by the operation of the switching circuit 40 so as toapply a voltage to the extended electrode 26D as shown in FIG. 6D, withthe result that the slider 3 is moved away from the first and secondstator electrodes 22A, 22B so as to be attracted toward the secondstator 2B, as shown in FIG. 5D.

Further, the voltage-applying electrode is switched from the extendedelectrode 26D to the second stator electrode 22B by the operation of theswitching circuit 40 so as to apply a voltage to the second statorelectrode 22B as shown in FIG. 6B, with the result that the slider 3 isattracted toward the first stator 2A by the electrostatic forcegenerated between the second stator electrode 22B and the first sliderelectrode 30A, as shown in FIG. 5E. Then, the voltage-applying electrodeis switched from the second stator electrode 22B to the extendedelectrode 26D by the operation of the switching circuit 40 so as toapply a voltage to the extended electrode 26D as shown in FIG. 6D, withthe result that the slider 3 is moved away from the second statorelectrode 22B so as to be attracted toward the second stator 2B.

Further, the voltage-applying electrode is switched from the extendedelectrode 26D to the second and third stator electrodes 22B, 22C by theoperation of the switching circuit 40 so as to apply a voltage to thesecond and third stator electrodes 22B, 22C as shown in FIGS. 6B and 6C,with the result that the slider 3 is attracted toward the first stator2A by the electrostatic force generated between the second and thirdstator electrodes 22B, 22C and the first slider electrode 30A. It shouldbe noted that, since a voltage is applied to both the second and thirdstator electrodes 22B and 22C, the slider 3 is attracted toward thefirst stator 2A such that the first slider electrode 30A is positionedto face the second and third stator electrodes 22B and 22C. Then, thevoltage-applying electrode is switched from the second and third statorelectrodes 22B, 22C to the extended electrode 26D by the operation ofthe switching circuit 40 so as to apply a voltage to the extendedelectrode 26D as shown in FIG. 6D, with the result that the slider 3 ismoved away from the second and third stator electrodes 22B, 22C so as tobe attracted toward the second stator 2B.

In the next step, the voltage-applying electrode is switched from theextended electrode 26D to the third stator electrode 22C by theoperation of the switching circuit 40 so as to apply a voltage to thethird stator electrode 22C as shown in FIG. 6C, with the result that theslider 3 is attracted toward the first stator 2A by the electrostaticforce generated between the third stator electrode 22C and the firstslider electrode 30A. Then, the voltage-applying electrode is switchedfrom the third stator electrode 22C to the extended electrode 26 d bythe operation of the switching circuit 40 so as to apply a voltage tothe extended electrode 26D as shown in FIG. 6D, with the result that theslider 3 is moved away from the second stator electrode 22B so as to beattracted toward the second stator 2B.

Then, the voltage-applying electrode is switched from the extendedelectrode 26D to the third and first stator electrodes 22C, 22A so as toapply a voltage to the third and first stator electrodes 22C, 22A asshown in FIGS. 6A and 6C, with the result that the slider 3 is attractedtoward the first stator 2A by the electrostatic force generated betweenthe third and first stator electrodes 22C, 22A and the first sliderelectrode 30A. It should be noted that, since a voltage is applied toboth the third and first stator electrodes 22C and 22A, the slider 3 isattracted toward the first stator 2A such that the first sliderelectrode 30A is positioned to face the third and first statorelectrodes 22C, 22A. Then, the voltage-applying electrode is switchedfrom the third and first stator electrodes 22C, 22A to the extendedelectrode 26D by the operation of the switching circuit 40 so as toapply a voltage to the extended electrode 26D as shown in FIG. 6D, withthe result that the slider 3 is moved away from the second and thirdstator electrodes 22C, 22A so as to be attracted toward the secondstator 2B.

As described previously, if a voltage is applied to the first statorelectrode 22A as shown in FIG. 6A, the slider 3 is attracted toward thefirst stator 2A by the electrostatic force generated between the firststator electrode 22A and the first slider electrode 30A.

As described above, a voltage is applied successively to the firststator electrode 22A, the extended electrode 26 d, both the first andsecond stator electrodes 22A and 22B, the extended electrode 26D, thesecond stator electrode 22B, the extended electrode 26D, both the secondand third stator electrodes 22B and 22C, the extended electrode 26D, thethird stator electrode 22C, the extended electrode 26D, both the thirdand first stator electrodes 22C and 22A, the extended electrode 26D, andthe first stator electrode 22A in the order mentioned, with the resultthat the slider 3 is moved in the direction denoted by the arrow inwhich the electrodes are arranged in the first stator 30A while theslider 3 is being slightly vibrated in a direction perpendicular to thedirection denoted by the arrow 24.

In the modified embodiment described above, the slider 3 is attractedfirst by one of the electrodes, e.g., the first stator electrode 22A,mounted to the first stator 2A and, then, the slider 3 is attracted bythe two adjacent electrodes, e.g., the first and second statorelectrodes 22A and 22B, with the result that the first slider electrode30A receives force that permits the first slider electrode 30A to bepositioned in substantially the center between the two adjacent statorelectrodes to which a voltage is applied. According to this drivingmethod, the force for driving the slider 3 in a direction crossing thedirection in which the slider 3 is moved is rendered relatively large,with the result that the movement of the slider is made smoother.

Incidentally, in the modified embodiment described above with referenceto FIG. 3 and FIGS. 5A to 5E, three electrodes are mounted to the firststator 2A. However, the present invention is not limited to theparticular modification. In other words, it is possible to mount morethan three electrodes, e.g., four electrodes, to the first stator 2A.FIG. 7 shows an electrostatic actuator according to a modifiedembodiment of the present invention, in which first to fourth statorelectrodes 22A to 22D are mounted, in place of the three first statorelectrodes shown in FIG. 3, to the first stator 2A and a single extendedelectrode 26D is mounted to the second stator 2B.

In the electrostatic actuator shown in FIG. 7, the fourth statorelectrode 24D is mounted to the first stator 2A in addition to the firstto third stator electrodes 22A, 22B, 22C shown in FIG. 3. These first tofourth stator electrodes 22A, 22B, 22C and 22D are arranged at the samepitch, and a plurality of slider electrodes 30A having the widthscorresponding to the widths of the four stator electrodes 22A, 22B, 22C,22D are arranged in the slider 3 in the forward direction. Also, theextended electrode 30D, which is uniform over the movable range of theslider 3, is mounted to the surface of the stator electrode 2B facingthe stator 2B.

As shown in FIG. 8, a voltage source 42 generating a voltage isconnected to the first, second, third and fourth stator electrodes 22A,22B, 22C, 22D, the extended electrode 26D, the first slider electrode30A and the second slider electrode 30D via the switching circuit 40serving to determine the timings of applying a voltage to these statorelectrodes 22A, 22B, 22C, 22D and the extended electrode 26D. Also, thefirst slider electrode 30A and the second stator electrode 30D areconnected to the ground through the switching circuit 40 or areconnected to negative potential point. As shown in FIG. 8, the switchingcircuit 40 comprises a stationary contacts 40A, 40B, 40C, 40D and astationary contact 40G connected to the ground, the stationary contactsbeing connected to the stator electrodes 22A, 22B, 22C, 22D and theextended electrode 26D, respectively, a first movable contact 40Fconnected to the voltage source 42, the circuit 40 being connected thesestator contacts 40A, 40B, 40C, 40D, and a second movable contact 40Econnected to the ground or to a negative voltage point. When one ofthese stationary contacts 40A, 40B, 40C, and 40B is connected to thevoltage source 42 through the movable contact 40F in the switchingcircuit 40 of the particular construction, the other stationary contacts40A, 40B, 40C, 40D are connected to the ground via the second movablecontact 40E or is connected to a negative potential point.

In this electrostatic actuator, a voltage is applied successively to thefirst stator electrode 22A, the extended electrode 26D, the secondstator electrode 22B, the extended electrode 26D, the third statorelectrode 22C, the extended electrode 26D, the fourth stator electrode22D, the extended electrode 26D and, then, the first stator electrode22A in the order mentioned, as described previously in conjunction withFIGS. 3 and 4A to 4E. As a result, the slider 3 is linearly moved in thedirection of the arrangement of the stator electrodes mounted to thefirst stator 2A, i.e., forward direction 24, on a macroscopic level,while the slider 3 is being vibrated in a direction crossing the forwarddirection on a microscopic level.

In the actuator shown in FIG. 8, it is possible to permit the slider 3to be moved slightly in the forward direction or the backward directionby applying the voltage to the stationary contacts 40A, 40B, 40C and 40Dat the timings shown in FIGS. 9A to 9F. To be more specific, the firstslider electrode 30A and the second slider electrode 30D are maintainedfirst at a low level voltage as shown in FIG. 9F, and a voltage isapplied to the first and second stator electrodes 22A and 22B as shownin FIGS. 9A and 9B. As a result, the slider 3 is attracted toward thefirst stator 2A by the electrostatic force generated between the statorelectrodes, (i.e., the first and second stator electrodes 22A, 22B) andthe first slider electrode 30A such that the first slider electrode 30Ais moved toward the first and second stator electrodes 22A, 22B. In thenext step, the switching circuit 40 is operated to change thevoltage-applying electrode from the first and second stator electrodes22A, 22B to the extended electrode 26D so as to apply a voltage to theextended electrode 26D, with the result that the slider 3 is moved awayfrom the third stator electrode 22C so as to be attracted toward thesecond stator 2B, as shown in FIG. 9D.

Then, the voltage-applying electrode is switched from the extendedelectrode 26D to the second and third stator electrodes 22B, 22C inaccordance with the operation of the switching circuit 40 so as topermit a voltage to be applied to the second and third stator electrodes22B, 22C as shown in FIGS. 9B and 9C, with the result that the slider 3is attracted toward the second stator 2A by the electrostatic forcegenerated between the stator electrodes (i.e., the second and thirdstator electrode 22B, 22C) and the fist slider electrode 30A. Then, thevoltage-applying electrode is switched from the second and third statorelectrodes 22B, 22C to the extended electrode 26D by the operation ofthe switching circuit 40 so as to permit a voltage to be applied to theextended electrode 26 d as shown in FIG. 9D, with the result that theslider 3 is moved away from the first and second stator electrodes 22A,22B so as to be attracted toward the second stator 2B.

Then, the voltage-applying electrode is switched from the extendedelectrode 26D to the third and fourth stator electrodes 22C, 22D inaccordance with the operation of the switching circuit 40 so as topermit a voltage to be applied to the third and fourth stator electrodes22C, 22D as shown in FIGS. 9C and 9D, with the result that the slider 3is attracted toward the first stator 2A by the electrostatic forcegenerated between the stator electrodes (i.e., the third and fourthstator electrodes 22C, 22D) and the first slider electrodes 30A as shownin FIG. 8. In the nest step, the voltage-applying electrode is switchedfrom the third and fourth stator electrodes 22C, 22D to the extendedelectrode 26D in accordance with the operation of the switching circuit40 so as to permit a voltage to be applied to the extended electrode26D, with the result that the slider 3 is moved away from the secondstator electrode 22B so as to be attracted toward the second stator 2Bas shown in FIG. 9D.

Further, the voltage-applying electrode is switched from the extendedelectrode 26D to the fourth and first stator electrodes 22D, 22A inaccordance with the operation of the switching circuit 40 so as topermit a voltage to be applied to the fourth and first stator electrodes22D, 22A, with the result that the slider 3 is attracted toward thefirst stator 2A by the electrostatic force generated between the statorelectrodes (i.e., the fourth and first stator electrodes 22D, 22A) andthe first slider electrode 30A. In the next step, the voltage-applyingelectrode is switched from the fourth and first stator electrodes 22D,22A to the extended electrode 26D in accordance with the operation ofthe switching circuit 40 so as to permit a voltage to be applied to theextended electrode 26D as shown in FIG. 9D, with the result that theslider 3 is moved away from the fourth and first stator electrodes 22D,22A so as to be attracted toward the second stator 2B.

In the electrostatic actuator shown in FIG. 7, it is possible to permita voltage to be applied to the first stator electrode 22A, the extendedelectrode 26 d, both the first and second stator electrodes 22A and 22B,the extended electrode 26D, the second stator electrode 22B, theextended electrode 26D, both the second and third stator electrodes 22Band 22C, the extended electrode 26D, the third electrode 22C, theextended electrode 26D, both the third and fourth stator electrodes 22Cand 22D, the extended electrode 26D, the fourth stator electrode 22D,the extended electrode 26D, both the fourth and first stator electrodes22D, 22A, the extended electrode 26, and the first stator electrode 22Ain the order mentioned. As a result, the slider 3 is linearly movedslightly in the arranging direction 24 of the electrodes mounted to thefirst stator 30A on the macroscopic level while the slider 3 is beingvibrated in the vertical direction on the microscopic level.

The driving force for operating the electrostatic actuator will now bedescribed briefly with reference to FIG. 8. The following descriptioncovers the case where the four stator electrodes 22A, 22B, 22C and 22Dare mounted. However, the present invention is not limited to the casewhere the four stator electrodes are mounted to the first stator. Inother words, a similar driving force is imparted to the slider 3 in thecase where the driving force is imparted from the stator, to which threestator electrodes or an n-number of stator electrodes are mounted, tothe slider 3.

The driving force, i.e., the generated force having a vertical componentFz and a horizontal component Fy, is represented by formulas (1) and (2)given below on the assumption that each of the slider 3 and the statorelectrodes 22A, 22B, 22C, 22D mounted to the stator 2 are parallel plateconductor electrodes that do not have a thickness:

Fz=n×∈SV ²/2d ²  (1)

Fy=n×∈LV ²/2d  (2)

where n denotes the number of slider electrodes 30A mounted to theslider 30A. The symbol ∈ denotes the dielectric constant between theslider 3 and each of the stator electrodes 22A, 22B, 22C, 22D mounted tothe stator 2A, the dielectric constant being represented by the productbetween the dielectric constant of vacuum and the dielectric constantbetween the slider electrode 30A and each of the stator electrodes 22A,22B, 22C, 22D mounted to the stator 2A. The dielectric constant ofvacuum is ∈0=8.85×10⁻¹² [N/m]. The relative dielectric constant is about1 for the air and about 3 for polyimide used for, for example,insulation of the electrode. Character S denotes the mutually facingarea between the slider electrode 30A and the stator electrodes 22A,22B, 22C, 22D, which extends in parallel to form parallel plates. Thearea S is determined by “w×L”, where w denotes the width of theelectrode sections mutually facing each other as shown in FIG. 8 (i.e.,the width along the side extending in the forward direction), and Ldenotes the length. Character v denotes the voltage applied between theelectrodes. Further, d denotes the distance between adjacent electrodes.The distance d corresponds to the gap Ga shown in FIG. 8.

Formulas (1) and (2) given above will now be considered under the statethat a voltage is applied between the stator electrodes 22C and 22D soas to be rendered active. Incidentally, the edge in the forwarddirection of the stator electrode 22C, i.e., the left edge, is definedas the reference position, which is the origin 0, and the forwarddirection is defined as positive, and the backward direction is definedas negative. Under the state that the left edge of the slider electrode30A shown in FIG. 8 is positioned leftward of the left edge of thestator electrode 22C, i.e., where the displacement X is larger than −L,the slider electrode 30A and the stator electrode 22C are not positionedto overlap each other, failing to form parallel plates. In this case,the component Fy of the generated force is rendered substantially zero.

On the other hand, when the left edge of the slider 3 is positioned tofall within a range between the negative length L and the origin 0relative to the left edge of the stator electrode 22C, as shown in FIG.8, i.e., where the displacement X is within a range of zero to −L, thecomponent Fy of the generated force is rendered constant regardless ofthe position of the left edge of the slider 3. This is because there isno component in formula (2) in the horizontal direction. Also, when theslider 3 is positioned remote from the origin 0 by a range within thelength L in the positive direction relative to the stator electrode 22C,i.e., where the displacement X is within a range of zero to +L, themagnitude of the generated force is rendered constant in the negativedirection. This is because the depth direction of the slider 3 neglectsthe influence on the generated force. Specifically, the influence of themutual function performed between the tapered portion of the sidesurface of the slider electrode 30A shown in FIG. 8 and the statorelectrodes 22A, 22B, 22C, 22D mounted to the stator 2A is neglected. Inthe actual actuator, it is necessary to take these influences intoconsideration. However, these influences are neglected in thedescription given above for the sake of brevity of the description.

FIG. 10 shows graphs I, II, III, IV and V relating to the generatedforce in the horizontal direction based on the situation describedabove. These graphs show by the finite-element method the changes in thegenerated force on the basis of the positional relationship between theslider 3 and the stator electrodes 22A, 22B, 22C, 22D mounted to thestator 2A. In the graph of FIG. 10, the generated force Fy in thehorizontal direction in unit of Newton (N), in which the forwarddirection is positive, is plotted on the ordinate. On the other hand,the positional relationship between the slider 3 and the statorelectrodes 22A, 22B, 22C, 22D mounted to the stator 2A, i.e., the valuesof displacement in which the forward direction is positive, is plottedon abscissa. In these graphs I, II, III, IV and V, the gap Ga shown inFIG. 8 is taken as a parameter, in which the gap Ga is 7.8 μm for graphII, 5.8 μm for graph III, 4.8 μm for graph IV, and 3.8 μm for graph V.The size of the electrostatic actuator for obtaining the graph of FIG.10 is determined on the assumption that the mechanism is used in mobileequipment such as a portable telephone or cellar phone. For example, thegap is set at 3.8 μm to 7.8 μm, L is set at 28 μm, w is set at 12 μm, Phis set at 16 μm, and the number of slider electrodes 30A mounted to theslider is set at 94.

As apparent from the graphs of FIG. 10, the generated force Fy in thehorizontal direction is gradually changed about the time when the sliderelectrode 30A of the slider 3 is moved to overlap with the statorelectrode 22C and about the time when the slider electrode 30A is movedaway from the stator electrode 22C. Incidentally, it is possible tosubstitute a sine wave waveform between the origin 0 and the point ofthe maximum value for the generated force Fy in the horizontaldirection. In FIG. 10, the voltage applied to the stator electrodes is acalculated value at 100V. According to the graphs shown in FIG. 10 andthe result of the study based on these graphs, the gap should fallwithin a range of between 3 μm and 10 μm, preferably between 3 μm and 5μm. It has been clarified that, if the gap falls within the range notedabove, it is possible to impart effectively the generated force Fy inthe horizontal direction to the slider 3.

Another modified embodiment of the electrostatic actuator of the presentinvention will now be described with reference to FIG. 11. Those membersof the actuator shown in FIG. 11 which are same as those shown in FIG. 3are denoted by the same reference numerals so as to avoid theoverlapping description.

FIG. 11 schematically shows the construction of an electrostaticactuator according to a modified embodiment of the present invention. Inthe electrostatic actuator shown in FIG. 11, the electrode width L ofthe slider electrode 30A of the slider 3 is set to fall within a rangeof between 1.5 times and 2.5 times as much as the width Wa of each ofthe first stator electrode 22A, the second stator electrode 22B and thethird stator electrode 22C mounted to the stator 2A. It follows that,within the range of the sliding movement of the slider 3, the sliderelectrode 30A is kept facing two of the first stator electrode 22A, thesecond stator electrode 22B and the third stator electrode 22C.

In the electrostatic actuator shown in FIG. 11, a signal voltage, whichcan be easily estimated based on the timing charts shown in FIGS. 9A and9F, is applied to the first to third stator electrodes 22A, 22B, 22C,the slider electrodes 30A, 30D and the extended electrode 26D.Therefore, the drawing relating to the signal voltage is omitted, andthe operation of the mechanism will now be described as follows.

In the first step, if a voltage is applied to the first and secondstator electrodes 22A, 22B, the slider 3 is attracted toward the stator2A, with the result that an acting force permitting the first and secondstator electrodes 22A, 22B to overlap with the first slider electrode30A of the slider 3 is generated between the stator electrodes 22A, 22Band the first slider electrode 30A. Then, if the voltage is applied tothe extended electrode 26D, the slider 3 is attracted toward the stator2B. Further, if voltage is applied to the second and third statorelectrodes 22B, 22C, the slider 3 is attracted toward the stator 2A asin the case where the voltage is applied to the first stator electrode22A and the second stator electrode 22B, with the result that the sliderelectrode 30A of the slider 3 receives the acting force so as to overlapwith the stator electrodes 22B, 22C. In other words, the voltage isrepeatedly applied to both the first and second stator electrodes 22A,22B, the extended electrode 26D, both the second and third statorelectrodes 22B, 22C, the extended electrode 26D, both the third andfirst stator electrodes 22C, 22A, the extended electrode 26D and, then,to both the first and second stator electrodes 22A, 22B in the ordermentioned. As a result, the slider 3 is linearly moved slightly in thearranging direction of the stator electrodes mounted to the first stator2A, i.e., in the forward direction 24, on the macroscopic level, whilethe slider 3 is being vibrate in a direction crossing the forwarddirection, on the microscopic level. It should also be noted that, ifthe voltage is repeatedly applied in the order opposite to the ordernoted above, i.e., if the voltage is applied first to both the statorelectrodes 22A, 22B, and, then, to the extended electrode 26D, both thesecond and third stator electrodes 22B, 22C, the extended electrode 26D,both the stator electrodes 22C, 22B, the extended electrode 26D, andthen to both the stator electrodes 22A, 22B in the order mentioned, theslider 3 is moved slightly in the backward direction.

In the modified embodiment shown in FIG. 11, the electrode width L ofthe slider electrode 30A mounted to the slider 3 is set to fall within arange of between 1.5 times and 2.5 times as much as the electrode widthWa of each of the stator electrodes mounted to the stator 2A asdescribed above. It should be noted in this connection that, if voltageis applied to both the stator electrodes 22B and 22C as shown in FIG.12A, an acting force BO having a component in the backward direction,which inhibits the forward movement, is also generated in addition tothe acting force FO having a component for moving the slider 3 in theforward direction 24. It follows that, in order to diminish the actingforce BO in the opposite direction as much as possible, it is desirablefor the electrode width L of the slider 3 to be small as shown in FIG.12B. However, if the electrode width L is small to make the total areaof the electrodes 30 excessively small, the acting force for vibratingthe slider 3 between the stators 2A and 3B is lowered. Also, thepositioning force for positioning the slider electrode 30A mounted tothe slider 3 in substantially the center between the adjacent statorelectrodes to which voltage is applied tends to be rendered unstable. Itfollows that, as a result of the study of the electrode width L of theslider 30 by the electromagnetic field analysis in view of the overallcomprehension of these situations, it has been found desirable to setthe electrode width L of the slider electrode 30A of the slider 3 tofall within a range of between 1.5 times and 2.5 times as much as theelectrode width Wa of each of the stator electrodes mounted to thestator 2B.

An electrostatic actuator according to another modified embodiment ofthe present invention will now be described with reference to FIGS. 13A,13B, 14A and 14B.

If voltage is applied to the stator electrode 22A of the stator 2A inthe construction shown in FIGS. 13A, 13B, the slider 3 receives anelectrostatic force (Coulomb force) so as to be attracted toward thestator 2A because of the electric field generated between the sliderelectrode 30A of the slider 3 and the stator electrode 22A of the stator2A. In this case, if the stator electrode 22A is brought into directcontact with the slider electrode 30A of the slider 3, an electric shortcircuit takes place so as to instantly destroy the electrode. Such beingthe situation, it is desirable to arrange the dielectric film 4 havingsufficient insulation breakdown strength between the stator electrode22A and the slider electrode 30A.

In the method of applying the voltage described above, a dielectricpolarization 5 takes place in the dielectric film 4 arranged in thevicinity of the stator electrode 22A on the side of the stator 2A, withthe result that the surface of the stator 2 is caused to bear a positivepotential relative to the slider electrode 30A. It follows that, even ifthe control is transferred to the next driving sequence, it is possiblefor the phenomenon that the slider is not driven toward the stator 2Bhaving the extended electrode 26B to take place. The particularphenomenon is the to be caused because an electrical inclination isbrought about within the dielectric film 4 by the dielectricpolarization. The residual potential caused by the dielectricpolarization is small. However, since the Coulomb force is inverselyproportion to the square of the distance between the electrodes, a largeacting force is imparted to the slider 3 even if the residual potentialis small under that state that the slider electrode 30A is onceattracted by the stator electrode 22A and, thus, the distance betweenthese two electrodes is small.

According to the modified embodiment shown in FIGS. 13A, 13B, 14A and14B, it is possible to realize a driving sequence that permitssuppressing the adverse effect of the dielectric polarization as much aspossible and to drive the slider 3 satisfactorily.

In the modified embodiment shown in FIGS. 13A and 13B, a potentialdifference is imparted between the stator electrode 22A of the stator 2Aand the slider electrode 30A of the slider 3 such that the potential ofthe stator electrode 22A is lower than that of the slider electrode 30Awhen the state that the slider 3 is attracted toward the statorelectrode 22A is changed into the next driving sequence in which voltageis applied to the extended electrode 26D. For example, if the potentiallevel of the slider 3 is set at zero, a potential difference is impartedbetween the stator electrode 22A and the slider electrode 30A such thatthe stator electrode 22A assumes a negative potential. If such apotential difference is imparted, the slider 3 is readily moved awayfrom the stator 2A so as to realize a smooth actuator function. Ifviewed macroscopically, the electric field formed between the statorelectrode 22A of the stator 2A and the corresponding slider electrode30A of the slider 3 because of the inclination of the remaining chargescaused by the dielectric polarization within the dielectric film 4 isopposite in direction to the electric field generated between thepotential newly applied to the stator electrode 22A, which is lower thanthe potential level of the slider electrode 30A, and the sliderelectrode 30A, with the result that these two electric fields nullifyeach other. If viewed microscopically, the phenomenon described abovecan be explained to the effect that the inclination of the residualcharge within the dielectric film 4 caused by the dielectricpolarization 5 is eliminated by the electric field formed by thepotential newly applied to the stator electrode 22A, the potential beinglower than the potential level of the slider electrode 30A.

For operating the actuator shown in FIGS. 13A and 13B, the voltagesignals as shown in FIGS. 14A to 14E are applied to the electrodesthrough the switching circuit 40. FIGS. 14A, 14B, and 14C show thetiming charts of signal voltages applied to the stator electrodes 22A,22B and 22C, respectively. FIG. 14D shows the timing chart of the signalvoltage applied to the stator electrode 26D. Further, FIG. 14E shows thevoltage applied to the slider electrodes 30A, 30D. The voltage shown inFIG. 14E, which is applied to the slider electrodes 30A, 30D is a groundpotential. The low level of the signal voltage applied to the statorelectrode 26D, which is shown in FIG. 14D, is has a low level of theground potential and a high level of a high potential. Also, the highlevel of each of the signal voltages applied to the stator electrodes22A, 22B, 22C, which are shown in FIGS. 14A, 14B and 14C, respectively,represents a high potential, and the low level is set at a negativepotential, with the intermediate level providing the ground potential.It follows that the slider electrode 3A is attracted to the statorelectrodes 22A, 22B and 22C by the attracting force when the voltagesignals shown in FIGS. 14A, 14B, 14C have a high level, and the sliderelectrode 3A is separated from the stator electrode 22A, 22B, 22C by therepulsive force when the when the voltage signals shown in FIGS. 14A,14B, 14C have a low level. Further, the slider electrode 30A does notreceive any acting force from the stator electrodes 22A, 22B, and 22Cwhen the voltage signals shown in FIGS. 14A, 14B, and 14C have anintermediate level.

Incidentally, it is possible for the potential of the slider electrode30A to be in a floating state that the slider electrode 30 is notelectrically connected to the ground. It is also possible to arrange adummy electrode connected to the ground in the vicinity of the slider 3so as to permit an electrostatic attractive force to the sliderelectrode 30A to exert effectively. Also, in the example shown in FIGS.13A and 13B, a dielectric film is arranged on the side of the stator 2A.Alternatively, it is possible to arrange the dielectric film 4 on theside of the slider 3 as shown in FIGS. 15A, 15B. The actuator shown inFIGS. 15A and 15B is operated similarly by the application of voltagesignals as shown in FIGS. 14A to 14E from the switching circuit 40 toeach of the electrodes.

The specific construction and the manufacturing method of anelectrostatic actuator according to another embodiment of the presentinvention will now be described with reference to FIGS. 16 and 17A to17C.

In the electrostatic actuator shown in FIG. 16, the slider 3 is formedin the form of a hollow cube. Slider electrodes 30A are arranged at apredetermined pitch on one outer plane 6 of the slider 3. The plane 6 ispositioned to face the stator electrodes 22A to 22C. Also, a lens 7 ofanother optical element is formed in one open portion of the slider 3.By the driving of the electrostatic actuator, the plane of the lens 7 ismoved forward or backward. In FIG. 16, the lens 7 is fixed to one openportion of the slider 3. Alternatively, it is also possible to mount thelens 7 on the other open portion opposite to the open portion shown inthe drawing. The slider 3 provided with the lens 7 and the sliderelectrodes 30A constituting the electrostatic actuator can bemanufactured by, for example, a glass molding technology. To be morespecific, it is possible for the lens 7 to be formed integral with theslider 3 such that a part of the slider 3 has a lens function.

The manufacturing method of the slider 3 of the electrostatic actuatorshown in FIG. 16 will now be described with reference to FIGS. 17A to17C.

In the first step, prepared is a block formed by the glass moldingtechnology, which is a hollow cube having the lens 7 formed on oneplane, i.e., the upper plane, as shown in FIG. 17A. Then, the slider 3is mounted with the lens 7 facing upward, as shown in FIG. 17A, and thelower plane facing the upper plane is in contact with a jig such a metalplate so as to permit the slider 3 to be fixed to the jig. Then, theside surface of the slider 3 is covered with a conductive material. Itis possible to employ any of a sputtering method, a vapor depositionmethod and a coating method as the covering method. By this covering,the five planes of the hollow cube are covered with the conductor filmexcept the lower plane that is in contact with, for example, a jig.Further, the conductor film is coated with a resist by, for example, aresist coating method, i.e., a so-called “spray system”, utilizing anelectrostatic attracting force. As a result, the five planes of thehollow cube are covered with the resist film except the lower plane thatis in contact with, for example, the jig.

In the next step, the slider 3 is detached from the jig or the like andis mounted to a jig (not shown) for patterning the electrodes on theslider 3. The jig for the electrode patterning has a housing section forhousing the slider 3, and the slider 3 is housed in the housing sectionof the jig such that one side surface of the slider 3 that is to bepatterned is exposed to the outside. The slider 3 housed in the housingsection is fixed to the jig for the electrode patterning without fail bythe mechanical pressing such as a spring or the like housed in thehousing section or by a suction mechanism provided with a negativepressure.

Incidentally, it is possible for the jig for the electrode patterning tohave a structure that permits mounting a plurality of sliders 3, e.g., astructure having a plurality of housing sections.

Then, a patterning transfer utilizing a photographic transfer system(i.e., a so-called “photo-fabrication technology) is applied to theexposed side surface so as to sensitize the resist. In the next step,the resist portion is etched so as to form a resist pattern of apredetermined pattern, thereby etching the conductive film, i.e., andthe metal portion, of the pattern thus formed, with the result that theconductive pattern alone of a predetermined pattern is left unremoved.

Incidentally, it is possible for the conductive material of theconductive film to consist of a transparent material such as ITO or anopaque material. Where a transparent material is used as the conductivematerial of the conductive film, the surface of the lens 7 is coveredsimply with the transparent layer and, thus, the transparent layer neednot be particularly removed. It follows that the manufacture of theslider 3 is finished by the etching step.

Where an opaque material is used as the conductive material of theconductive film, the slider 3 is detached from the jig for the electrodepatterning before the etching step, and the slider 3 is mounted again tothe jig for the electrode patterning with the plane of the lens 7 facingupward. Then, a pattern transfer utilizing a photographic transfersystem (which is a so-called “photo-fabrication technology”) is appliedby using an optical mask (which is generally reticule in thesemiconductor process) so as to expose the resist film covering the filmof the conductive material formed on the plane of the lens 7. Then, theresist portion is removed by etching, followed by removing the metalportion by etching, thereby finishing preparation of the slider 3. Inthis embodiment, the resist film is positive type, which is melted afterthe resist film is exposed with light. However, the resist film may benegative type, in which unexposed portion or portions are melted afterthe resist film is exposed with light.

Incidentally, the slider electrode 30A of the slider 3 is electricallyconnected to all the four side surfaces including the portion patternedin a ladder shape. In place of forming the ladder-shaped sliderelectrode 30A, it is possible to provide an irregular shape in whichprojections and recesses are repeated at a pitch P on the surface and tocover the entire surface with a film of a conductive material.

It is also possible to arrange a region 8, in which the ladder-shapedelectrodes are not positioned, in a part of the plane 6 in which theladder-shaped electrodes 30A are formed as shown in FIG. 16, in order toprevent the slider 3 from being brought into direct contact with thestator electrodes 22A, 22B, 22C mounted to the stator and with theextended electrode 26D. In this case, it is desirable to permit astopper 10 mounted to the slider 3 to abut against the region 8 as shownin FIGS. 18A and 18B. To be more specific, the stopper 10 having athickness larger than the thickness, i.e., the height, of the statorelectrodes 22A, 22B, 22C is arranged on the surface regions of thestators 2A, 2B facing the regions 8, as shown in FIGS. 18A and 18B. Thestopper 10 is allowed to abut against the region 8 by the vibration ofthe slider 3 and to slide along the region 8. As a result, it ispossible to prevent the slider electrodes 30A, 30B of the slider 3 frombeing brought into contact with the stator electrodes 22A, 22B, and 22Cof the stator 2A and with the extended electrode 26D of the stator 2B.It should be noted that it is also possible for the stopper 10 to bemounted on the side of the slider 3 such that the stopper 10 is broughtinto contact with the region in which the electrodes of the stators 2Aand 2B are not mounted, as shown in FIGS. 19A and 19B.

As described above, the slider can be manufactured easily by themanufacturing method described above, making it possible to realize anelectrostatic actuator rich in mass production capability and capable ofbeing manufactured with a low cost.

Another construction of an electrostatic actuator of the presentinvention and the manufacturing method thereof will now be describedwith reference to FIG. 20. In the electrostatic actuator shown in FIG.20, a box-like member 52D open on both sides facing each other isprepared as a stator 2B. Also, a lid-like member 52C closing the upperopening of the box-shaped member 52D is prepared as a stator 2A. Itshould be noted that the stator electrodes 22A, 22B, 22C of the stator2A are formed on the inner surface of the box-shaped member 52D, and theextended electrode 26D of the stator 2B is formed on the inner surfaceof the lid-like member 52C. These two members 52C, 52D are combined asshown in FIG. 20 and bonded to each other so as to prepare a statorstructure 2 provided with electrodes arranged a predetermined distanceapart from each other and imparting a predetermined clearance betweenthe stator structure 2 and the slider 3. Before assembly of the statorstructure 2, the slider 3 is arranged in advance within the box-shapedmember 52D, followed by bonding these two members 52C and 52D to eachother so as to finish preparation of the electrostatic actuator.

The stator 2 having a high accuracy can be prepared by a molding method.Specifically, the stator structure 2 having a void portion having alongitudinal axis in the driving direction of the slider can be easilyprepared by manufacturing parts of the stator structure 2 by processinga plate material by punching or a pressing as a mold formation. It isalso possible to manufacture the stator structure 2 having theelectrodes arranged at a predetermined distance apart from each otherwith a high accuracy. Incidentally, in the structure shown in FIG. 20,the uniform extended electrode 26D is formed on the inner surface of thestator structure 52C. However, it is also possible to form the extendedelectrode 26D on the stator structure 52D, with the stator electrodes22A, 22B, 22C being formed on the stator structure 52C.

Several constructions relating to the stator included in theelectrostatic actuator of the present invention and the manufacturingmethod thereof will now be described with reference to FIGS. 21A, 21B,21C, 22A, 22B, 22C, 22D, 23A, 23B and 23C.

FIG. 21A is a plan view showing the stator of the electrostaticactuator. FIGS. 21B and 21C are cross sectional views along the line B—Bshown in FIG. 21A and along the line A—A shown in FIG. 21A,respectively. As shown in FIG. 21A, a substrate 11 used as the stator 2Ahas a surface facing the slider 3, and the first to third statorelectrodes 22A, 22B, 22C are formed on the surface facing the slider 3.As shown in FIG. 21C, a glass substrate or a silicon substrate having aninsulating film such as a silicon oxide film formed thereon is used asthe substrate 11. FIG. 21A shows three sets of the first to third statorelectrodes 22A to 22C. The first stator electrode 22A and the thirdstator electrode 22C are arranged to form a comb-shaped configurationtogether with the wirings connected to these stator electrodes. Thesecond stator electrode 22B is arranged between the first statorelectrode 22A and the third stator electrode 22C, and the wiringextending from the second stator electrode 22B is arranged on theinsulating film formed on the wiring extending from the first statorelectrode 22A, as shown in FIG. 21B. Further, the wiring extending fromthe second stator electrode 22B extends via the insulating layer so asto reach the region of an edge portion of the substrate 11 outside thefirst stator electrode 22A. The wiring is connected to a terminal formedon the surface on which each stator electrode is formed and in theregion in the side portion of the surface.

The stator 3 shown in FIG. 21A is manufactured through the process shownin FIGS. 22A to 22D.

In the first step, prepared is the substrate 11 as shown in FIG. 22A.Formed on the substrate 11 are the stator electrode 22A, the wiringportion for the stator electrode 22A, the stator electrode 22C, thewiring portion for the stator electrode 22C, the stator electrode 22B,and the wiring for the stator electrode 22B arranged outside the wiringportion for the stator electrode 22A. These stator electrodes and thewirings are formed of a metallic material 12 such as an aluminum film.Then, an insulating film 13 is formed on the substrate 11 as shown inFIG. 22B. Also, through-holes 14 for connecting the wiring portion ofthe stator electrode 22B formed outside the wiring portion of the statorelectrode 22A to the stator electrode 22B are formed in the wiringportion of the stator electrode 22B arranged outside the wiring portionof the stator electrode 22A and in a predetermined position of thestator electrode 22B. For forming the insulating film, it is possible touse silicon oxide, silicon nitride or polyamide depending on themanufacturing process. Then, formed is a wiring 15 for connecting thewiring portion of the stator electrode 22B positioned outside the wiringportion of the stator electrode 22A to the stator electrode 22B, asshown in FIG. 21C. Further, an insulating film 16 is formed as requiredon the wiring 15 serving to connect the wiring portion of the statorelectrode 22B positioned outside the wiring portion of the statorelectrode 22A to the stator electrode 22B.

It should be noted that the wiring for connecting the wiring portion ofthe stator electrode 22B to the stator electrode 22B is formed on theupper side of the wiring for the stator electrode 22A with theinsulating film interposed therebetween. By contraries, it is alsopossible to form the wiring serving to connect the wiring portion forthe stator electrode 22B to the stator electrode 22B below the wiringfor the stator electrode 22A with an insulating layer interposedtherebetween. Incidentally, the wiring portion for the stator electrode22B is formed on the insulating film in the construction describedabove. Alternatively, it is also possible for the wiring portion to beconnected by a wire bonding in place of the use of the wiring portionformed on the insulating film so as to permit the wiring portion for thestator electrode 22A to be electrically connected to the wiring portionfor the stator electrode 22B.

In the embodiment described above, the first to third stator electrodesare formed on the substrate 11 constituting the stator. However, thepresent invention is not limited to the particular construction. Forexample, it is possible to form a plurality of sets of the first tofourth stator electrodes 22A to 22D on the substrate 11, as shown inFIGS. 23A to 23C.

Still additional construction of the stator incorporated in theelectrostatic actuator of the present invention will now be describedwith reference to FIGS. 24A to 24C.

FIG. 24A is a plan view showing the construction of the stator 2, andFIGS. 24B and 24C are cross sectional views along the lines B—B and A—A,respectively, shown in FIG. 24A. As shown in FIGS. 24A to 24C, thewirings connected to the stator electrodes 22A to 22C are electricallyinsulated from each other and extend to regions in the side portions ofthe substrate 11. The end portions of these wirings extend intothrough-holes extending to reach the back surface of the substrate 11 soas to be connected to the terminals formed on the back surface of thesubstrate 11. In the substrate 11 of the particular construction, it ispossible to apply voltage from the terminals on the back surface of thesubstrate to the stator electrodes 22A to 22C, making it possible toincrease the degree of freedom in the arrangement of the circuit.

The constructions relating to the stators of the electrostatic actuatorof the present invention will now be described with reference to FIGS.25A to 25D. FIG. 25A is a plan view showing the construction of thestator, FIGS. 25B and 25C are cross sectional views along the lines B—Band A—A, respectively, shown in FIG. 25A, and FIG. 25D is a back view ofthe substrate 11.

In the construction of the stator shown in FIGS. 25A to 25D, the statorelectrodes 22A to 22C are arranged in parallel on the substrate 11. Thewirings connected to the stator electrodes 22A to 22C extend linearly,and the terminals at the ends of the extended portions of the wiringsare connected to the terminals arranged on the back surface of thesubstrate 11. In the substrate 11 of the particular construction, it ispossible to apply voltage from the terminals arranged on the backsurface of the substrate to the stator electrodes 22A to 22C, making itpossible to increase the degree of freedom in the arrangement of thecircuit.

Further, the construction relating to the stators included in theelectrostatic actuator of the present invention will now be describedwith reference to FIGS. 26A to 26D, 27D, and 28A to 28C. In theconstruction of the stators included in the electrostatic actuatoraccording to this embodiment of the present invention, a secondsubstrate 11B shown in FIGS. 27A to 27D is bonded to a first substrate11A shown in FIGS. 26A to 26D so as to prepare the construction of thestator shown in FIGS. 28A to 28C.

FIG. 26A is a plan view of the substrate 11A, FIGS. 26B and 26C arecross sectional views along the lines B—B and A—A, respectively, shownin FIG. 26A, and FIG. 26D is a back view of the substrate 11 a. In thesubstrate 11A shown in FIGS. 26A to 26D, the stator electrodes 22A to22C are arranged on the substrate 11 in parallel. The wirings connectedto the stator electrodes 22A to 22C extends linearly so as to beconnected to the terminals, and terminals of the wirings are connectedto the terminals arranged on the back surface of the substrate 11 viathe through-holes extending through the substrate 11. The terminalscorresponding to the stator electrodes 22A to 22C are electricallyconnected to a common terminal, as shown in FIG. 26D. Also, a connectionterminal that is to be connected to the common terminal as shown in FIG.27A is formed on a second substrate 11B shown in FIGS. 27A to 27D. Thecommon terminal is connected to a connection terminal formed on the backsurface of the substrate 11B via a through-hole extending through thesubstrate 11B. The back surface of the first substrate 11A and the frontsurface of the second substrate 11B are bonded to each other so as topermit the common terminal and the connection terminal to be bonded toeach other, thereby manufacturing a stator structure as shown in FIGS.28A to 28C.

The specific manufacturing method of the stator structure shown in FIGS.28A to 28C will now be described. In the first step, through-holescorresponding to the stator electrodes 22A to 22D are formed inpredetermined regions of the substrate 11A. By forming terminals inthese through-holes, the terminals are connected to the wiringsconnected to the stator electrodes 22A to 22C. It is possible to formconcave portions in those regions of the substrate 11A in which theterminals are formed and to form through-holes within these concaveportions. In this case, the terminals connected to the wirings extendingfrom the stator electrodes 22A to 22C are arranged within thethrough-holes such that the terminals corresponding to the statorelectrodes 22A to 22C are connected to each other within the concaveregions. By forming the concave portions on the back surface of thesubstrate 11A, a clearance between the substrate 11A and the othersubstrate 11B is not generated even if the substrate 11B is bonded tothe back surface of the substrate 11A, making it possible to bring thesubstrates 11A and 11B into a sufficient contact by the bonding.

Incidentally, it is possible for the through-hole not to extend throughthe substrate 11A. In other words, it is possible to form a concaveportion having a depth large enough to form a through-hole in thesubsequent step of polishing the substrate 11A.

The substrate 11A having a through-hole formed therein is bonded to thesubstrate 11B. Where the substrates are formed of a silicon substrateand a glass substrate, an anodic bonding method can be employed for thesubstrate bonding. Where silicon substrates are bonded to each other, itis possible to employ a suitable method depending on the kind of thesubstrate such as a water glass method. It is possible for athrough-hole or a wiring for the lead of the wiring to be formed inadvance in the substrate 11B that is to be bonded. In the substrate 11prepared by bonding two substrates, the substrate 11 is polished untilthe substrate 11A has a predetermined thickness. After the polishingstep, the through-hole is allowed to extend through the substrate 11A.Then, the wirings for the stator electrodes 22A to 22C are formed on thepolished surface of the substrate 11A so as to connect the terminals ofthe wirings to the wirings on the back surface of the substrate 11A.

Further, where the terminals within the through-holes and the wiringsthat are to be connected to these terminals are not formed in advance onthe side of the substrate 11B, these terminals and the wirings areformed, followed by connecting the substrate 11A to the wirings of thesubstrate 11B so as to finish preparation of the stator 2.

In the manufacturing process described above, there is a merit on theprocess that it suffices for the processing depth of the through-holeformed in the substrate 11A to be small. Also, the through-hole isformed by the general isotropic processing. In other words, if it isintended to form a through-hole in a certain depth direction, thelateral processing is also performed in the same amount. As a result,the diameter φ of the through-hole that can be formed is limited by thethickness of the substrate through which the through-hole extends,giving rise to a limit in forming a plurality of through-holes close toeach other. The limitation provides an obstacle in making fine thearranging pitch of the electrodes corresponding to the electrodes of theslider formed on the surface of the substrate 11A. In the manufacturingprocess described above, it is possible to expect a prominent effectthat the arranging pitch of the surface electrodes of the substrate 11can be made sufficiently small. Incidentally, in this embodiment, thewiring of the electrodes formed on the surface of the substrate 11A inthe other embodiments is formed on the back surface of the substrate11A. However, it is possible to form the wiring section on the surfaceof the substrate 11B.

Another construction relating to the stator included in theelectrostatic actuator of the present invention will now be describedwith reference to FIGS. 29A to 29D. FIG. 29A is a plan view showing theconstruction of the stator 2, FIGS. 29A and 29C are cross sectionalviews along the lines B—B and A—A, respectively, shown in FIG. 29A, andFIG. 29D is a back view of the substrate 11.

In the stator structure shown in FIGS. 29A to 29D, an SOI substrate isused as the substrate 11 of the stator 2, and each electrode is formedof bulk silicon. A silicon structure 19 forming each electrode is formedon one surface of the SOI substrate 11 by using, for example, a DRIEapparatus. It is possible to further form an insulating film (not shown)on the surface of the silicon structure 19.

A through-hole 20 for taking out the electrode is formed on the backsurface of the substrate, and a terminal acting as an electrodeconnected to the silicon structure is arranged within the through-hole.

As a modification of the structure shown in FIGS. 29A to 29D, it ispossible for each electrode to be formed of a Ni structure in place ofthe silicon structure.

In the manufacturing process of the modification, a metal layer forminga seed layer of plating is formed on the oxidized silicon substrate. Athick resist film is formed on the substrate, and the resist film thusformed is exposed to light, followed by a developing process, therebyforming a mold structure for forming an electrode structure. Then, a Nilayer forming the electrode structure is formed by an electroplatingmethod, followed by removing the thick resist film and subsequentlyapplying an insulating film coating. Through these steps, the process ofmanufacturing the electrode structure is finished. In this manufacturingprocess, an adjusting step for adjusting the stator structure, e.g., thesurface polishing step, is performed as desired.

Incidentally, a through-hole for taking out the electrode is formed onthe back surface of the substrate like the structure shown in FIGS. 29Ato 29D, and a terminal is arranged within the through-hole and theterminal thus arranged is connected to the electrode structure and isconnected to the wiring on the back surface.

An application to which the electrostatic actuator of the presentinvention is applied will now be described with reference to FIG. 30.

The electrostatic actuator of the present invention is excellent in itsdriving characteristics and, thus, is adapted for use in a focusadjusting mechanism of a small camera.

FIG. 30 shows a module portion of a small camera having theelectrostatic actuator of the present invention mounted thereto. Asshown in FIG. 30, a CMOS or a CCD is mounted on a substrate 21, and anelectrostatic actuator 22 is mounted thereon. A slider integral with thecamera is used as the slider included in the electrostatic actuator.Also, an IC such as a DSP for controlling the driving of theelectrostatic actuator is mounted on the substrate 21.

The camera module of the particular construction can be used as a cameraunit included in, for example, a portable telephone or a digital camera.

As described above, the present invention provides an electrostaticactuator that can be manufactured at a low cost and is adapted for themass production.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A camera module for photographing a pictureimage, comprising: an image pick-up element; and an electrostaticactuator mechanism mounted to the image pick-up element, theelectrostatic actuator mechanism including: a first stator provided withan electrode group including at least three electrodes successivelyarranged in a predetermined direction, voltage being applied to theelectrodes respectively; a second stator arranged to face the firststator and provided with an electrode extending in the predetermineddirection; a movable member arranged between the first stator and thesecond stator, and provided with a first electrode section facing theelectrode group, a second electrode section facing the electrodeextending in the predetermined direction, and an optical elementconfigured to form an optical image on the image pick-up element; and aswitching circuit configured to apply voltage alternately to at leastone of the electrodes forming the electrode group and the electrodeextending in the predetermined direction, the potential of at least oneof the electrodes forming the electrode group being rendered higher thanthe potential of the first electrode section, or the potential of theelectrode extending in the predetermined direction being rendered higherthan the potential of the second electrode section, and to switch theorder of applying voltage successively to at least one of the electrodesof the electrode group.
 2. The camera module according to claim 1,wherein the switching circuit applies voltage simultaneously to at leasttwo electrodes forming the electrode group adjacent to each other in thepredetermined direction.
 3. The camera module according to claim 1,wherein a width in the predetermined direction of the first electrodesection mounted to the movable member is 1.5 to 2.5 times as much as awidth in the predetermined direction of each of the electrodes formingthe electrode group.
 4. The camera module according to claim 1, furthercomprising a dielectric film formed to cover the electrode group.
 5. Thecamera module according to claim 4, wherein the switching circuit isconfigured to impair a potential difference such that the potential ofat least one of the electrodes forming the electrode group is renderedlower than the potential of the first electrode section, when voltage isapplied to the electrode extending in the predetermined direction. 6.The camera module according to claim 1, further comprising a dielectricfilm formed to cover the first electrode section.
 7. The camera moduleaccording to claim 6, wherein the switching circuit is configured toimpair a potential difference such that the potential of at least one ofthe electrodes forming the electrode group is rendered lower than thepotential of the first electrode section, when voltage is applied to theelectrode extending in the predetermined direction.
 8. The camera moduleaccording to claim 6, wherein the first and second electrode sectionsbear substantially the ground potential.
 9. The camera module accordingto claim 1, wherein the optical element is driven together with themovable member.
 10. The camera module according to claim 1, wherein thefirst and second stators include stoppers projecting from upper surfacesof the electrode group and the electrode extending in the predetermineddirection, and the movable member is provided with regions in which thestoppers are slid, the regions being formed on surfaces on which thefirst and second electrode sections are formed.
 11. The camera moduleaccording to claim 1, wherein the movable member includes stoppersprojecting from surfaces of the first and second electrode sections, andthe first and second stators are provided with regions in which thestoppers are slid, the regions being formed on surfaces on which theelectrode group and the electrode extending in the predetermined areformed.
 12. The camera module according to claim 1, wherein theelectrode group includes three electrodes to which voltage is appliedrespectively.
 13. The camera module according to claim 1, wherein theelectrode group includes four electrodes to which voltage is applied.14. The camera module according to claim 4, wherein the first and secondelectrode sections bear substantially the ground potential.